1. Field of the Invention
This invention relates to the deformable mirrors which upon replacement of a component, can repeat the pre-replacement mirror surface contour thereof.
2. The Prior Art
Deformable mirrors are employed to correct distorted beams of various kinds, e.g., of white light, UV light, or laser beams. A problem has been that once the desired mirror contour is found and an actuator of a prior art deformable mirror, such as shown in FIG. 1, must be replaced, the compression spring can inflict permanent deformation on the face plate and mirror surface thereof to the detriment of the reflected beam and require a repair measure such as re-polishing of the mirror surface, as more fully discussed below.
The prior art does not appear to suggest a solution to this problem. For example, U.S. Pat. No. 3,904,274 to Feinleib (1975) discloses a mirror with piezoelectric actuators therein which are not replaceable. U.S. Pat. No. 4,679,915 to Kriz et al. (1987), teaches a deformable mirror having columns of electrical actuators which are pre-stressed by a threaded bolt 39 (FIG. 1), rather than being pre-stressed by a spring, e.g., spring 28 of FIG. 2 herein, so that mirror deformation caused by spring unloading does not arise.
There is also a German Patent DE 3502024 Al to Herrmann (1986) which discloses manual, pneumatic, axial adjustment of the pressure on piezoelectric actuators and release thereof. However, such application and release of pneumatic pressure is done individually and can result in mirror distortion by pressure differential between the respective actuators.
It appears that the closest prior art is illustrated in FIG. 2 herein, wherein replacement of an actuator will result in compression spring expansion and distortion forces applied to the face plate and mirror surface that can be permanent, as more fully discussed below.
The reason that a compression preload on the actuator is needed in the first place, is as follows. An actuator such as a piezoelectric stack, can, by application of a voltage to the wafers in the stack, cause such wafers to thicken and extend the length of the stack and thus the length of the actuator so as to push on a contour post and deform the mirror surface outwardly. However, upon discontinuance of such voltage there-across, such stack contracts and a countering, compressive force or preload, on such contour post, is needed to enable such post to maintain contact with such stack and follow it as it recedes so as to deform (or contour) the mirror surface inwardly when desired. Accordingly such actuator is resiliently preloaded, e.g., per the spring of FIG. 2, to enable the mirror surface (and contour post) to move axially back and forth with the actuator. However, in the prior art, when an attempt is made to remove an actuator for replacement purposes, the preload spring expands, causing deformation to the mirror surface as discussed above. Another problem is that the replacement actuator may be of greater or lesser length than the previous one and upon installation, causes further distortion to the face plate and mirror surface.
Accordingly, there is a need and market for compression release and decoupling of mirror components such as an actuator that avoids permanent deformation to the mirror surface and overcomes the above prior art shortcomings.
There has now been discovered a preloaded deformable mirror wherein components, such as actuators, can be removed and returned or replaced with another actuator, without permanent damage to the mirror surface and in a manner so as to repeat the pre-substitution mirror surface deformation or contour. That is, mirror polishing or other repair procedures are avoided or made unnecessary, by the pre-loaded deformable mirror of the present invention.